A bicycle is normally provided with a rear derailleur associated with the pinion group, which consists of a series of coaxial toothed wheels (crowns), having different diameters and numbers of teeth, integral with the hub of the rear wheel.
A bicycle is typically also provided with a front derailleur associated with the chainset, which consists of a series of toothed wheels (crowns) having different diameters and numbers of teeth, associated with a shaft of the crank axle rotated by a pair of pedals.
In both cases, the derailleur engages a transmission chain extending in a closed ring between the pinion group and the chainset, moving it on to sprockets having different diameters and number of teeth, so as to obtain different transmission ratios.
In particular, downward gearshifting or downshifting refers to when the chain passes from a sprocket having a larger diameter to a sprocket having a smaller diameter, and upward gearshifting or upshifting refers to when the chain moves from a sprocket having a smaller diameter to a sprocket having a greater diameter. In this respect, it should be noted that with reference to the front derailleur, downward gearshifting corresponds to the passage to a lower transmission ratio and upward gearshifting corresponds to the passage to a higher transmission ratio, vice-versa with reference to the rear derailleur, downward gearshifting corresponds to the passage to a higher transmission ratio and upward gearshifting corresponds to the passage to a lower transmission ratio.
The movement in the two directions of a derailleur is obtained through an actuation device mounted to allow easy operation for the cyclist, i.e. normally on the handlebars, close to the handlebar grip where the brake lever for commanding the braking of the front or rear wheel is also located. Control devices that allow both a derailleur to be driven in the two directions and a brake to be controlled are, as mentioned above, commonly known as integrated controls.
Customarily, the actuation device of the front derailleur and the brake lever of the front wheel are located by the left-hand grip of the handlebars, and vice-versa the actuation device of the rear derailleur and the brake lever of the rear wheel are located by the right-hand grip.
More specifically, in a mechanical gearshift, each derailleur is moved between the sprockets, in a first direction by a traction action exerted by a normally sheathed inextensible cable (commonly known as Bowden cable), in an opposite second direction by the release of the traction of the cable and/or by the elastic return action of a spring provided in the derailleur itself.
Normally, the direction in which the movement is determined by the release of the traction of the cable and/or by the return spring is that of downward gearshifting; vice-versa, the traction action of the control cable takes place in the direction of upward gearshifting, in which the chain moves from a sprocket having a smaller diameter to a sprocket having a larger diameter.
In the actuation device, the control cable is actuated in traction or in release through winding and unwinding on a rotor element, commonly known as cable-winding drum, the rotation of which is controlled by the cyclist by a pair of suitable control levers.
In any case, the actuation device must provide that the drum be held still in rotation in a number of predetermined angular positions, corresponding to the different positions of the derailleur required by the different ratios, i.e. on the different sprockets of the transmission. Therefore, the actuation device of a front derailleur has a relatively low number of predetermined angular positions (typically three), corresponding to the positions of the front derailleur on the different crowns of the chainset; a rear gearshift, on the other hand, has a relatively high number of predetermined angular positions (typically from seven to ten), corresponding to the positions of the rear derailleur on the different pinions.
So called “release-type” actuation systems are known in which the rotation of the cable-winding drum, where the cable is wound up, takes place as a result of the physical effort exerted by the cyclist on the appropriate upshift lever, whereas the rotation in the opposite direction is obtained by actuating the downshift lever, substantially freeing the cable-winding drum and allowing a return spring, which can be that of the derailleur as well as a return spring connected to the cable-winding drum inside the mechanism itself, to act in the direction to unwind the cable from the drum, clearly in a controlled manner.
A first release-type device is one in which the downshift lever is in the form of a button. The drum is kept in fixed position by a pawl that engages the teeth present on the outer surface of the cable-winding drum. The pressing of the button keeps the cable-winding drum locked in position while it allows the disengagement of the pawl from the teeth of the drum. The subsequent release towards the neutral rest position of the button allows the free rotation of the drum under the thrust of a coil spring mounted coaxial to the drum, while simultaneously the pawl engages the subsequent tooth of the cable-winding drum, locking it in the new position after the desired angular rotation.
A first drawback of such a device is that downward gearshifting is not sufficiently quick upon actuation by the cyclist, since it does not take place when the button is pressed but rather essentially in the step of releasing the button.
Another drawback is that to effect multiple downshifts, it is necessary to carry out multiple individual consecutive downward gearshifting operations.
A second release-type device is one in which the cable-winding drum is kept in position by a lever that engages at its first end the teeth present on the outer surface of the cable-winding drum. The thrusting actuation of the downshift lever allows the disengagement of the first end of the lever from the teeth of the cable-winding drum, the free rotation of the cable-winding drum for an amount of rotation equal to about half the desired rotation and the engagement of the second end of the lever on the teeth of the outer surface of the drum. The subsequent release of the downshift lever towards the neutral rest position determines the free rotation of the cable-winding drum for the second amount of rotation, which completes gearshifting, and the reengagement of the first end of the lever on the outer teeth of the drum.
In such a device downward gearshifting is also not sufficiently quick upon actuation by the cyclist, since it takes place substantially in two steps corresponding to the pushing and to the release of the lever and gearshifting is complete only after release of the downshift lever and its return to the neutral rest position.
As in the previous example, another drawback is that to effect multiple downshifts, it is necessary to carry out multiple individual consecutive downward gearshifting operations.
So called “active-type” actuation devices are also known in which the rotation of the cable-winding drum both in the sense of winding of the cable and in the sense of unwinding of the cable takes place by the physical force exerted by the cyclist on the appropriate upshift and downshift levers or by a servomechanism activated by the cyclist.
A known active-type device is one in which upshift and downshift levers act by actively thrusting on the cable-winding drum to place it in rotation for the entire angular extension defined between two adjacent gearshift positions. In particular, to carry out downward gearshifting, the lever must be rotated until the cable-winding drum reaches its desired final position, where it is locked in position by an indexing means.
A first drawback of such a device is that downward gearshifting is not sufficiently quick upon actuation by the cyclist, since it is only completed when the downshift lever has carried out a sufficient rotation to take the cable-winding drum into the final position.
Another drawback is that if the downshift lever is not pushed by a sufficiently large angle to take the cable-winding drum in rotation into the new gearshifting position, gearshifting is not completed and the derailleur remains in a disadvantageous intermediate position between two sprockets.
The problem at the basis of the invention is that of allowing quicker and more precise gearshifting operations to be carried out compared to known actuation devices.